fix(playground-ui): remove default temperature and topP from studio agent settings (#12256)

## Summary

- Remove hardcoded `temperature: 0.5` and `topP: 1` defaults from
playground agent settings
- Let agent config and provider defaults handle these values instead

## Problem

Studio was applying its own defaults for temperature and topP, which
broke Claude Opus/Sonnet models that don't allow both to be specified
simultaneously. The previous fix attempted to detect Claude 4.5+ models
and reactively clear topP, but this was racy - the API request would
fire before the `useEffect` ran.

## Solution

The cleaner fix is to not set playground defaults at all. If neither the
agent nor the user explicitly sets temperature/topP, the playground just
doesn't send them, letting the provider use its own defaults.

## Test plan

- [x] Tested with `examples/agent-v6` using Claude Opus 4.5 - no longer
errors
- [x] Unit tests updated and passing

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Bug Fixes**
* Agent settings no longer include hardcoded temperature and topP
defaults; these now defer to agent configuration and provider defaults.

* **Tests**
* Unit tests updated to expect temperature and topP to be undefined by
default.

* **Chores**
  * Changeset added documenting the behavioral change and patch release.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: CalebBarnes <CalebBarnes@users.noreply.github.com>
Co-authored-by: Marvin Frachet <marvin@mastra.ai>

Author: CalebBarnes

.changeset/smooth-bananas-give.md

@@ -0,0 +1,6 @@
+---
+'@mastra/playground-ui': patch
+---
+
+Remove hardcoded temperature: 0.5 and topP: 1 defaults from playground agent settings
+Let agent config and provider defaults handle these values instead

packages/playground-ui/src/domains/agents/hooks/__tests__/use-agent-settings-state.test.ts

@@ -24,28 +24,24 @@ import { isAnthropicModelWithSamplingRestriction } from '../../utils/model-restr
 /**
  * Test file for use-agent-settings-state.ts
  *
- * Issue #11760: Anthropic Claude 4.5+ models fail when both temperature and topP are sent.
- * Anthropic's API returns: "`temperature` and `top_p` cannot both be specified for this model."
- *
- * Default settings include both temperature and topP for models that support both (OpenAI, Google, Claude 3.5).
- * For Claude 4.5+ models, the AgentSettings component auto-clears topP when the model is detected.
+ * Default settings should NOT include temperature or topP - these should be
+ * left undefined so models use their provider defaults unless explicitly set.
  */
 describe('use-agent-settings-state defaults', () => {
   beforeEach(() => {
     localStorageMock.clear();
     vi.clearAllMocks();
   });
 
-  it('should have both temperature and topP set by default (for models that support both)', async () => {
+  it('should not have temperature or topP set by default (use model provider defaults)', async () => {
     const { defaultSettings } = await import('../use-agent-settings-state');
 
     const modelSettings = defaultSettings.modelSettings;
 
-    // Defaults should include both values for models that support them
-    // (OpenAI, Google, Claude 3.5, etc.)
-    // Claude 4.5+ models will have topP auto-cleared at the component level
-    expect(modelSettings.temperature).toBe(0.5);
-    expect(modelSettings.topP).toBe(1);
+    // temperature and topP should be undefined to use model provider defaults
+    // This also avoids Claude 4.5+ errors where both cannot be specified
+    expect(modelSettings.temperature).toBeUndefined();
+    expect(modelSettings.topP).toBeUndefined();
   });
 });
 

packages/playground-ui/src/domains/agents/hooks/use-agent-settings-state.ts

@@ -10,8 +10,6 @@ export const defaultSettings: AgentSettings = {
   modelSettings: {
     maxRetries: 2,
     maxSteps: 5,
-    temperature: 0.5,
-    topP: 1,
     chatWithGenerateLegacy: false,
     chatWithGenerate: false,
   },